Genome blasts open rice research

Researchers have sequenced the genome of the world's most devastating rice fungus, opening the door to the development of crops that can resist infection.

The fungus, called Magnaporthe grisea, is responsible for rice blast, a disease that destroys enough rice to feed 60 million people each year. "That's a very conservative estimate," says plant pathologist Ralph Dean, who has studied the fungus for more than a decade at North Carolina State University in Raleigh. The fungus particularly affects rice in hot and humid countries such as Thailand and the Philippines.

With the pathogen’s global impact in mind, Dean and his colleagues set their sights on obtaining the genetic sequence of the rice-blast fungus seven years ago. In combination with the DNA sequence of rice itself, which researchers established in 2002, the team hopes the code will facilitate the development of genetically modified rice capable of resisting the disease.

"I equate this to a battlefield. The key to any battle is to understand the strength and weaknesses of your enemy," Dean explains.

Spore war

Using standard laboratory techniques for genome sequencing, the team determined that the rice-blast fungus has more than 11,000 genes. The work, reported in Nature1, marks the completion of the first draft sequence of a plant pathogen.

Importantly, the code reveals that M. grisea uses a new class of receptor to distinguish its target, rice, from other crops. These receptors are found on the infectious spores of the fungus, which can aggressively punch into the leaves of rice plants.

The team notes that identification of these receptors is a major step on the path to fighting the fungus. Such information could be used, for example, to create rice that disguises itself from these receptors.

At the moment, powerful fungicides are the only option for keeping M. grisea at bay. Some farmers have fallen ill through exposure to high doses of these fungicides. Genetically engineered rice would reduce the need for such toxic chemicals, the researchers say.